Transcription-Maturation of pre mRNA Posttranscriptional Modifications

Maturation of Pre mRNA (Primary Transcript)

Free online Biochemistry Lectures for Medical students by Biochemistry Club

• In the previous lesson we discussed the formation of  The Eukaryotic pre-mRNA.
• The pre-mRNA leaves the nucleus nucleus and enters into the cytoplasm to get translated.
• But before it is translated it must undergo the maturation process.
• This Maturation involves 3 main steps:

1. Capping
2. Splicing
3. Poly Adenylation

Co Transcriptional and Post Transcriptional Modifications

Capping, Splicing & Polyadenylation of mRNA

• The pre-mRNA can also be called as a Primary transcript but it is not a mature mRNA  yet.
• The Introns in the pre-mRNA have to be spliced out in order to mature.
• Pre-mRNA has to be capped also.
• The Cap is placed at the 5′ end of the mRNA and
• Finally a Poly A tail is added on the 3′ end to the pre-mRNA.
• These 3 maturation steps must take place.
• The cap at the 5′ end of the mRNA is called the 7-Methyl Guanosine Cap.
• This Cap is added Co-Transcriptionally,
• This cap is very unique as there is a specific Tri-phosphate linkage that links the cap at 5′ end.
• This Linkage provides protection to the mRNA from getting damaged by enzymes. 
• The other important function of this cap is to identify the mRNA, so that the rRNA and tRNA can recognize it and ribosome can bind to it for translation to occur.
• There is also an addition of a bunch of As to the 3′ end of the mRNA.
• This Poly A Tail has 2 functions:
  1. It provides protection to the mRNA like the cap
  2. It helps the mRNA to get out in the cytoplasm.

FOR COMPLETE LESSON ALONG WITH FIGURES FOR BETTER UNDERSTANDING, CLICK BIOCHEMISTRY II TAB ON THE HOME PAGE, THEN IN THE DROP DOWN MENU CLICK GENETICS. WHEN THE PAGE OPENS CLICK CURRICULUM TO VIEW ALL THE LESSONS. CLICK THE LESSON OF YOUR CHOICE.